Erase block data splitting

ABSTRACT

A Flash memory device, system, and data handling routine is detailed with a distributed erase block sector user/overhead data scheme that splits the user data and overhead data and stores them in differing associated erase blocks. The erase blocks of the Flash memory are arranged into associated erase block pairs in “super blocks” such that when user data is written to/read from the user data area of a sector of an erase block of the super block pair, the overhead data is written to/read from the overhead data area of a sector of the other associated erase block. This data splitting enhances fault tolerance and reliability of the Flash memory device.

RELATED APPLICATIONS

This Application is a divisional of U.S. application Ser. No.11/489,321, filed Jul. 19, 2006, now U.S. Pat. No. 7,545,682, issuedJun. 9, 2009, which application is a divisional of U.S. application Ser.No. 11/004,454, filed Dec. 3, 2004, now U.S. Pat. No. 7,193,899, issuedMar. 20, 2007, which application is a divisional of U.S. applicationSer. No. 10/602,991, filed Jun. 24, 2003, now U.S. Pat. No. 6,906,961,issued Jun. 14, 2005, and all of which applications are commonlyassigned and incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to integrated circuits and inparticular the present invention relates to data management of Flashmemory devices.

BACKGROUND OF THE INVENTION

Memory devices are typically provided as internal storage areas in thecomputer. The term memory identifies data storage that comes in the formof integrated circuit chips. There are several different types of memoryused in modern electronics, one common type is RAM (random-accessmemory). RAM is characteristically found in use as main memory in acomputer environment. RAM refers to read and write memory; that is, youcan both write data into RAM and read data from RAM. This is in contrastto ROM, which permits you only to read data. Most RAM is volatile, whichmeans that it requires a steady flow of electricity to maintain itscontents. As soon as the power is turned off, whatever data was in RAMis lost.

Computers almost always contain a small amount of read-only memory (ROM)that holds instructions for starting up the computer. Unlike RAM, ROMcannot be written to. An EEPROM (electrically erasable programmableread-only memory) is a special type non-volatile ROM that can be erasedby exposing it to an electrical charge. EEPROM comprise a large numberof memory cells having electrically isolated gates (floating gates).Data is stored in the memory cells in the form of charge on the floatinggates. Charge is transported to or removed from the floating gates byspecialized programming and erase operations, respectively.

Yet another type of non-volatile memory is a Flash memory. A Flashmemory is a type of EEPROM that can be erased and reprogrammed in blocksinstead of one byte at a time. A typical Flash memory comprises a memoryarray, which includes a large number of memory cells. Each of the memorycells includes a floating gate field-effect transistor capable ofholding a charge. The data in a cell is determined by the presence orabsence of the charge in the floating gate. The cells are usuallygrouped into sections called “erase blocks”. The memory cells of a Flashmemory array are typically arranged into a “NOR” architecture (each celldirectly coupled to a bitline) or a “NAND” architecture (cells coupledinto “strings” of cells, such that each cell is coupled indirectly to abitline and requires activating the other cells of the string foraccess). Each of the cells within an erase block can be electricallyprogrammed in a random basis by charging the floating gate. The chargecan be removed from the floating gate by a block erase operation,wherein all floating gate memory cells in the erase block are erased ina single operation.

FIG. 1 shows a simplified diagram of a Flash memory subsystem 134 of theprior art. In the Flash memory subsystem 134, a Flash memory controller130 is coupled 132 to one or more Flash memory devices 100. The Flashmemory controller 130 contains a control state machine 110 that directsthe operation of the Flash memory device(s) 100; managing the Flashmemory array 112 and updating internal RAM control registers and tables114 and the non-volatile erase block management registers and tables128. The RAM control registers and tables 114 are loaded at power upfrom the non-volatile erase block management registers and tables 128 bythe control state machine 110. The Flash memory array 112 of each Flashmemory device 100 contains a sequence of erase blocks 116. Each eraseblock 116 contains a series of sectors 118 that are typically eachwritten to a single row of the memory array 112 and include a user dataspace or area 120 and an associated control or overhead data space orarea 122. The control/overhead data space 122 contains overheadinformation for operation of the sector it is associated with. Suchoverhead information typically includes, but is not limited to, eraseblock management (EBM) data, sector status information, or an errorcorrection code (ECC, not shown). ECC's allow the Flash memory 100and/or the Flash memory controller 130 to detect data errors in the userdata space 120 and attempt to recover the user data if possible.

The user data space 120 in each sector 118 is typically one or moremultiples of 512 bytes long (depending on memory array 112 row size),wherein one or more logical operating system (OS) sectors of 512 byteseach or multiple logically addressed data words can be stored on the rowor sector 118. In a typical Flash memory device 100 each erase block 116typically contains 16 or more physical sectors 118. Each new 512 bytesof user data and its associated overhead data are together written intoan available erase block sector 118 (i.e., User data A with Overheaddata A within a single erase block sector 118) as the user data arrivesat the Flash memory 100. User data is typically written sequentiallyinto the sectors 118 of an erase block 116 until it is filled. It isnoted that other configurations of Flash memory subsystems 134, havingFlash memory devices 100 and Flash memory controllers 130, are wellknown in the art, including such devices that integrate the functions ofthe separate Flash memory controller and Flash memory device into asingle device.

A problem with Flash memories is that each erase block sector 118 storesthe user data and the overhead information, which includes the errorcorrection codes, within close proximity to each other or,alternatively, on the same physical row of the memory array 112. Becauseof this, an error in one or more sectors 118 of an erase block 116 ofthe Flash memory 100 due to physical damage, impurity migration, writefatigue, electrical transients, or another reason can also affect theoverhead data associated with those sectors. This increases thelikelihood of a loss of data (if the ECC is damaged also) or even theloss of the ability to access the affected sector occurring (if thesector management data is damaged) when such an error happens.

For the reasons stated above, and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art fora Flash memory device or Flash memory handing routine that has a faulttolerant erase block sector architecture and data/overhead informationstorage method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 details a prior art Flash memory.

FIGS. 2A and 2B detail memory systems with Flash memory in accordancewith embodiments of the present invention.

FIG. 3 details an erase block super block pair of a Flash memory inaccordance with an embodiment of the present invention.

FIGS. 4A, 4B, 4C, and 4D detail sector write/read order of an eraseblock super block of a Flash memory in accordance with embodiments ofthe present invention.

FIG. 5 details a NAND Flash erase block sector of an embodiment of thepresent invention.

FIGS. 6A and 6B detail sector write/read order of an erase block superblock of a NAND architecture Flash memory in accordance with anembodiment of the present invention.

FIG. 7 details a data splitting control circuit in accordance with anembodiment of the present invention.

FIGS. 8A and 8B detail a split data ECC circuit in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration specific preferredembodiments in which the inventions may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is to be understood that otherembodiments may be utilized and that logical, mechanical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined only by the claims and equivalents thereof.

To improve data reliability in Flash memories, a Flash memory device,system, or data handling routine in accordance with an embodiment of thepresent invention splits the user data from the associated overheaddata, storing each in separate Flash memory devices, differing eraseblocks, or differing sectors of an erase block in a distributedapproach. This avoids the issue of potential corruption of both the userdata and overhead data due to each being held within close proximity toeach other or on the same wordline (row) in the same erase block sector.A Flash memory embodiment of the present invention stores the user datain the user data area of a sector of an erase block and the associatedoverhead data in the overhead data area of a sector of a different eraseblock. This provides separation of the user data and its associatedoverhead data, allowing for an increased possibility of data recovery incase of a corruption of the user data and/or overhead data stored ineither erase block. In one embodiment of the present invention a Flashmemory has a sequence of paired erase blocks (super blocks), such thatthe overhead data areas of the sectors of each erase block of an eraseblock super block pair are stored in the paired companion erase block.In another embodiment of the present invention a Flash memory has asequence of paired erase blocks and a dedicated hardware system toautomatically read/write user data from/to one erase block of an eraseblock pair and read/write the associated overhead data from/to theoverhead data area of the companion erase block to improve the speed ofthe user data/overhead data splitting operation. In another embodimentof the present invention a Flash memory has a state machine or firmwarecontrol of erasure of paired erase blocks of a super block pair andstate machine/firmware control of allocation of newly erased super blockerase block pairs for use. In yet another embodiment of the presentinvention a Flash memory replaces a set of paired erase blocks that havebecome damaged by allocating spare replacement erase blocks in areplacement super block under hardware control. In a further embodimentof the present invention a Flash memory replaces one erase block of aset of paired erase blocks that have become damaged by allocating aspare replacement erase block under firmware control. In anotherembodiment of the present invention a NAND Flash memory has a datasplitting controller that generates data splitting addresses from astart address. In yet another embodiment, an ECC circuit generatesread/write ECC data in a data splitting configuration.

As stated above, the two common types of Flash memory arrayarchitectures are the “NAND” and “NOR” architectures, so called for thesimilarity each basic memory cell configuration has to the correspondinglogic gate design. In the NOR array architecture, the floating gatememory cells of the memory array are arranged in a matrix similar to RAMor ROM. The gates of each floating gate memory cell of the array matrixare coupled by rows to word select lines (word lines) and their drainsare coupled to column bit lines. The source of each floating gate memorycell is typically coupled to a common source line. The NOR architecturefloating gate memory array is accessed by a row decoder activating a rowof floating gate memory cells by selecting the word line coupled totheir gates. The row of selected memory cells then place their storeddata values on the column bit lines by flowing a differing current if ina programmed state or not programmed state from the coupled source lineto the coupled column bit lines. A column page of bit lines is selectedand sensed, and individual data words are selected from the sensed datawords from the column page and communicated from the Flash memory.

A NAND array architecture also arranges its array of floating gatememory cells in a matrix such that the gates of each floating gatememory cell of the array are coupled by rows to word lines. However eachmemory cell is not directly coupled to a source line and a column bitline. Instead, the memory cells of the array are arranged together instrings, typically of 8, 16, or more each, where the memory cells in thestring are coupled together in series, source to drain, between a commonsource line and a column bit line. This allows a NAND Flash arrayarchitecture to have a higher memory cell density than a comparable NORFlash array, but with the cost of a generally slower access rate andprogramming complexity.

A NAND architecture floating gate memory array is accessed by a rowdecoder activating a row of floating gate memory cells by selecting theword select line coupled to their gates. In addition, the word linescoupled to the gates of the unselected memory cells of each string arealso driven. However, the unselected memory cells of each string aretypically driven by a higher gate voltage so as to operate them as passtransistors and allowing them to pass current in a manner that isunrestricted by their stored data values. Current then flows from thesource line to the column bit line through each floating gate memorycell of the series coupled string, restricted only by the memory cellsof each string that are selected to be read. This places the currentencoded stored data values of the row of selected memory cells on thecolumn bit lines. A column page of bit lines is selected and sensed, andthen individual data words are selected from the sensed data words fromthe column page and communicated from the Flash memory.

Because all the cells in an erase block of a Flash memory device must beerased all at once, one cannot directly rewrite a Flash memory cellwithout first engaging in a block erase operation. Erase blockmanagement (EBM), typically under the control of an internal statemachine or device firmware, provides an abstraction layer for this tothe host (a processor or an external memory controller), allowing theFlash device to appear as a freely rewriteable device, including, butnot limited to, managing the logical address to physical erase blocktranslation mapping for reads and writes, the assignment of erased andavailable erase blocks for utilization, and the scheduling erase blocksthat have been used and closed out for block erasure. Erase blockmanagement also allows for load leveling of the internal floating gatememory cells to help prevent write fatigue failure. Write fatigue iswhere the floating gate memory cell, after repetitive writes anderasures, no longer properly erases and removes charge from the floatinggate. Load leveling procedures increase the mean time between failure ofthe erase block and Flash memory device as a whole.

In many modern Flash memory device implementations, the host interfaceand erase block management routines additionally allow the Flash memorydevice to appear as a read/write mass storage device (i.e., a magneticdisk) to the host. One such approach is to conform the interface to theFlash memory to be identical to a standard interface for a conventionalmagnetic hard disk drive allowing the Flash memory device to appear as ablock read/write mass storage device or disk. This approach has beencodified by the Personal Computer Memory Card International Association(PCMCIA), Compact Flash (CF), and Multimedia Card (MMC) standardizationcommittees, which have each promulgated a standard for supporting Flashmemory systems or Flash memory “cards” with a hard disk drive protocol.A Flash memory device or Flash memory card (including one or more Flashmemory array chips) whose interface meets these standards can be pluggedinto a host system having a standard DOS or compatible operating systemwith a Personal Computer Memory Card International Association—AdvancedTechnology Attachment (PCMCIA-ATA) or standard ATA interface. Otheradditional Flash memory based mass storage devices of differing lowlevel formats and interfaces also exist, such as Universal Serial Bus(USB) Flash drives.

Many of the modern computer operating systems, such as “DOS” (DiskOperating System), were developed to support the physicalcharacteristics of hard drive structures; supporting file structuresbased on heads, cylinders and sectors. The DOS software stores andretrieves data based on these physical attributes. Magnetic hard diskdrives operate by storing polarities on magnetic material. This materialis able to be rewritten quickly and as often as desired. Thesecharacteristics have allowed DOS to develop a file structure that storesfiles at a given location which is updated by a rewrite of that locationas information is changed. Essentially all locations in DOS are viewedas fixed and do not change over the life of the disk drive being usedtherewith, and are easily updated by rewrites of the smallest supportedblock of this structure. A sector (of a magnetic disk drive) is thesmallest unit of storage that the DOS operating system supports. Inparticular, a sector has come to mean 512 bytes of information for DOSand most other operating systems in existence. Flash memory systems thatemulate the storage characteristics of hard disk drives are preferablystructured to support storage in 512 byte blocks along with additionalstorage for overhead associated with mass storage, such as ECC (errorcorrection code) bits, status flags for the sector or erase block,and/or redundant bits.

FIG. 2A is a simplified diagram of a computer system 240 thatincorporates a Flash memory device 200 embodiment of the presentinvention. In the computer system 240 of FIG. 2A, the Flash memory 200is coupled to a processor 202 with an address 204, control 206, and databus 208. Internally to the Flash memory device, a control state machine210 directs internal operation of the Flash memory device; managing theFlash memory array 212 and updating RAM control registers and tables214. The Flash memory array 212 contains a sequence of erase blocks 216,226 arranged in paired sets of erase blocks. Each erase block 216, 226contains a series of sectors 218, 234 that contain a user data space220, 230 and a control/overhead data space 222, 232. The overhead dataspace 222, 232 contains overhead information for operation of the sector218, 234, such as an error correction code (not shown), status flags, oran erase block management data field area (not shown). The RAM controlregisters and tables 214 are loaded at power up from the non-volatileerase block management registers and tables 228 by the control statemachine 210. The user data space 220 in each sector 218 is typically 512bytes long. In a Flash memory device 200 embodiment of the presentinvention each erase block 216 typically contains 128 sectors 218. It isnoted that other formats for the erase blocks 216, 226 and sectors 218,234 are possible and should be apparent to those skilled in the art withbenefit of the present disclosure.

FIG. 2B is a simplified diagram of another computer system 290 thatincorporates a Flash memory system 250 embodiment of the presentinvention. In the computer system 290 of FIG. 2B, the Flash memorysystem 250, such as a memory system or Flash memory card, is coupled toa processor 252 with an address 254, control 256, and data bus 258.Internal to the Flash memory system 250, a memory controller 260 directsinternal operation of the Flash memory system 250; managing the Flashmemory devices 262, directing data accesses, updating internal controlregisters and tables (not shown), and/or directing operation of otherpossible hardware systems (not shown) of the Flash memory system 250,such as a hardware data splitter. The memory controller 260 is coupledto and controls one or more Flash memory devices 262 via an internalcontrol bus 286. It is noted that other architectures Flash memorysystems 250, external interfaces 254, 256, 258, and manners of couplingthe memory controller 260 to the Flash memory devices 262, such asdirectly coupled individual control busses and signal lines, arepossible and should be apparent to those skilled in the art with benefitof the present disclosure.

The Flash memory devices 262 contain a sequence of erase blocks 266, 276in internal memory arrays. Each erase block 266, 276 contains a seriesof sectors 268, 284 that contain a user data space 270, 280 and acontrol/overhead data space 272, 282. The overhead data space 272, 282contains overhead information for operation of the sector 268, 284, suchas an error correction code (not shown), status flags, or an erase blockmanagement data field area (not shown). In a Flash memory system 250embodiment of the present invention each Flash memory device 262 hastheir erase blocks 266, 276 internally arranged in paired sets of eraseblocks (superblocks). In another Flash memory system 250 embodiment ofthe present invention paired sets of erase blocks 266, 276 (superblocks)are arranged across two or more Flash memory devices 262. It is notedthat other formats and pairings for Flash memory devices 262, eraseblocks 266, and sectors 268 are possible and should be apparent to thoseskilled in the art with benefit of the present disclosure.

FIG. 3 further details an example of a super block 300 of one possiblesector format for a Flash memory embodiment of the present invention. InFIG. 3, a pair of erase blocks (Erase Block N and Erase Block N+Y, wheretypically Y is an offset, and all user accessible erase blocks of theFlash memory array are paired) 302, 304 are paired together into a superblock 300. Each erase block 302, 304 of the super block pair 300 hassectors 0 through x for x+1 total sectors in each erase block 302, 304.Each sector having a user data area 306 and an overhead data area 308.

When user data 306 is written to a selected sector m 310, 312 of anerase block 302, 304 of the super block 300, the overhead data generatedfor the user data is written into the overhead data area 306 of anotherselected sector m 310, 312 of the other erase block 302, 304 of theerase block super block pair 300. For example, User Data A written tothe user data area 314 of Sector m 310 of Erase Block N 302 will haveits Overhead Data (Ovhd A) written to the overhead data area 316 ofSector m 312 of Erase Block N+Y 304; User Data B written to the userdata area 320 of Sector m 312 of Erase Block N+Y 304 will have itsOverhead Data (Ovhd B) written to the overhead data area 318 of Sector m310 of Erase Block N 302.

When user data 306 is read from a selected sector m 310, 312 of an eraseblock 302, 304 of the super block 300, the overhead data for the userdata is read from the overhead data area 308 of another selected sectorm 310, 312 of the other erase block 302, 308 of the erase block pair300. For example, User Data A read from the user data area 314 of Sectorm 310 of Erase Block N 302 will have its Overhead Data (Ovhd A) readfrom the overhead data area 316 of Sector m 312 of Erase Block N+Y 304;User Data B read from the user data area 320 of Sector m 312 of EraseBlock N+Y 304 will have its Overhead Data (Ovhd B) read from theoverhead data area 318 of Sector m 310 of Erase Block N 302.

It is noted that the relative addresses of the erase blocks 302, 304that make up the super block pair 300 (Erase Block N 302 and Erase BlockN+Y 304) within a Flash memory are arbitrary and can be selected to gainthe most architectural advantage for the Flash memory. It is also notedthat the relative address of the selected sector m 310, 312 thatcontains user data to the relative address of the other sector m of theassociated erase block 302, 304 of the super block 300 pair thatcontains the associated overhead data for the user data is alsoarbitrary and has multiple possible methods of mapping. These methodsinclude, but are not limited to, using the same sector address in bothassociated erase blocks 302, 304 of the super block pair 300, using asector address m for user data and sector address x−m for overhead data,or using sector address m for user data and sector address m+1 foroverhead data. It is noted that other arrangements for writing andreading split user 306 and associated overhead 308 data from twoseparate sectors 310, 312 each from separate associated erase blocks302, 304 of a super block pair 300 are possible and should be apparentto those skilled in the art with benefit of the present disclosure.

In the Flash memory embodiment of the present invention detailed in FIG.2A, when user data is written to a sector 218, 234 of an erase block216, 226 of the Flash memory 200, the overhead data generated for theuser data is written into the overhead data area 222, 232 of a sector218, 234 of the associated erase block 216, 226 of the erase block superblock pair. For example, User Data A written to the user data area 220of Sector 0 218 of Erase Block 0 216 will have its Overhead Data (OvhdA) written to the overhead data area 232 of Sector 0 234 of Erase Block1 226; User Data B written to the user data area 230 of Sector 0 228 ofErase Block 1 226 will have its Overhead Data (Ovhd B) written to theoverhead data area 222 of Sector 0 218 of Erase Block 0 216.

When user data is read from a sector of an erase block of the Flashmemory 200, the overhead data for the user data is read from theoverhead data area of a sector of the associated erase block of theerase block super block pair. For example, User Data A read from theuser data area 220 of Sector 0 218 of Erase Block 0 216 will have itsOverhead Data (Ovhd A) read from the overhead data area 232 of Sector 0234 of Erase Block 1 226; User Data B read from the user data area 230of Sector 0 228 of Erase Block 1 226 will have its Overhead Data (OvhdB) read from the overhead data area 222 of Sector 0 218 of Erase Block 0216.

Dedicated data splitting circuitry 224 is utilized in one Flash memory200 embodiment of the present invention to automate the split of theuser data and overhead data and to improve the operation of writing orreading the split user/overhead data from each erase block super blockpair of the Flash memory array 212. This dedicated data splittinghardware 224 eliminates the need for these operations to be handled bythe control state machine/firmware 210 and thus reduces the access timepenalty of splitting the user data and overhead data. The erase blocks216, 226 of the Flash memory 200 are erased and allocated in pairs bythe control state machine/firmware 210. Erase block erasure of Flashmemory 200 embodiments of the present invention also are generally doneunder control of the control state machine/firmware 210, as theoperation is infrequent and of a relatively long duration, reducing itstime criticality.

FIG. 4A is a simplified diagram of a super block pair 400 showing onemethod of data write/read access sequences to an embodiment of thepresent invention. In FIG. 4A, the super block 400 contains a paired setof associated erase blocks (Erase Block N and Erase Block N+Y) 402, 404.Each erase block 402, 404 containing a sequence of erase block sectors414 having a user data area 406, 410 and an overhead data area 408, 412.

When data is written to/read from the associated erase blocks 402, 404of the super block 400 of FIG. 4A, each sector of data is sequentiallywritten to/read from the associated erase blocks 402, 404 of the superblock 400 in a manner that alternates accesses to each erase block 402,404. Thus, the next sector 414 to be written/read in the super block 400of FIG. 4A is selected from the erase block 402, 404 that was not lastwritten/read. For example, 2 kilobytes of data (alternatively, 4 sectorsof data) written to the super block pair 400 of FIG. 4A starting on aneven erase block address is written/read in the order (sequence 1, 2, 3,4, 5, 6, 7, and 8) 416 as shown. In FIG. 4A, the first sequential sectorof user data is written or read from the super block 400 starting withthe user data area 406 of Sector 0 of Erase Block N 402. The overheaddata area 412 of Sector 0 of Erase Block N+Y 404 is then written/readfor the overhead data associated with the first sequential sector ofuser data. The second sequential sector (the next sector) of user datawritten to/read from the super block 400 is then written to/read fromthe user data area 410 of Sector 0 of Erase Block N+Y 404 and theassociated overhead data is written to/read from the Sector 0 overheaddata area 408 of Erase Block N 402. The third sequential sector of userdata written to/read from the super block 400 is written to/read fromthe user data area 406 of Sector 1 of Erase Block N 402 and theassociated overhead data is written to/read from the Sector 1 overheaddata area 412 of Erase Block N+Y 404. The fourth sequential sector (thefinal 512 byte sector of the 2 kilobytes of user data) of user datawritten to/read from the super block 400 is then written to/read fromthe user data area 410 of Sector 1 of Erase Block N+Y 404 and theassociated overhead data is written to/read from the Sector 1 overheaddata area 408 of Erase Block N 402.

For 2 kilobytes of data (alternatively, 4 sectors of data) written tothe super block pair 400 of FIG. 4A starting on an odd erase blockaddress, the user data is written/read in the example order (secondsequence 1, 2, 3, 4, 5, 6, 7, and 8) 418 as shown, starting at sectoraddress 3. In FIG. 4A, the first sequential sector of user data iswritten or read from the super block 400 starting with the user dataarea 410 of Sector 3 of Erase Block N+Y 404. The overhead data area 408of Sector 3 of Erase Block N 402 is then written/read for the overheaddata associated with the first sequential sector of user data. Thesecond sequential sector (the next sector) of user data written to/readfrom the super block 400 is then written to/read from the user data area406 of Sector 4 of Erase Block N 402 and the associated overhead data iswritten to/read from the Sector 4 overhead data area 412 of Erase BlockN+Y 404. The third sequential sector of user data written to/read fromthe super block 400 is written to/read from the user data area 410 ofSector 4 of Erase Block N+Y 404 and the associated overhead data iswritten to/read from the Sector 4 overhead data area 408 of Erase BlockN 402. The fourth sequential sector (the final 512 byte sector of the 2kilobytes of user data) of user data written to/read from the superblock 400 is then written to/read from the user data area 406 of Sector5 of Erase Block N 402 and the associated overhead data is writtento/read from the Sector 5 overhead data area 412 of Erase Block N+Y 404.

FIG. 4B is a simplified diagram of a super block pair 450 showinganother method of data write/read access sequences to an embodiment ofthe present invention. In FIG. 4B, the super block 450 contains a pairedset of associated erase blocks (Erase Block N and Erase Block N+Y) 452,454. Each erase block 452, 454 containing a sequence of erase blocksectors 464 having a user data area 456, 460 and an overhead data area458, 462.

When data is written to/read from the associated erase blocks 452, 454of the super block 450 of FIG. 4B, each sector of data is sequentiallywritten to/read from an erase block 452, 454 in a sequential manner andthe overhead data placed in the overhead data area 458, 462 of the otherassociated erase block 452, 454 of the super block pair 450. Once theselected erase block 452, 454 of the super block pair 450 is entirelyfilled/read, user data is written to/read from the other associatederase block 452, 454 of the super block pair 450 and the overhead datais stored in the overhead data areas 458, 462 of the first erase block452, 454.

For example, user data is written to/read from the super block pair 450of FIG. 4B in the order (sequence 1, 2, 3, and 4; A, B, C, and D) 466 asshown. In FIG. 4B, the first sequential sector of user data is writtenor read from the super block 400 starting with the user data area 456 ofSector 0 of Erase Block N 452 (for write/read sequence 1, 2, 3, and 4).The overhead data associated with the first sequential sector of userdata is then written to/read from the overhead data area 462 of Sector 0of Erase Block N+Y 454. The second sequential sector (the next sector)of user data written to/read from the super block 450 is then writtento/read from the user data area 456 of the next sequential sector 464(Sector 1) of Erase Block N 452 and the associated overhead data iswritten to/read from the next sequential sector (Sector 1) overhead dataarea 462 of Erase Block N+Y 454. User data and associated overhead datais written to/read from the erase blocks 452, 454 of super block 450 inthis manner until all the user data areas 406 of the sectors 464 ofErase Block N 452 have been utilized or all its utilized sectors 464read.

User data is placed into/read from the user data areas 460 of EraseBlock N+Y 454 of the super block pair 450 in a similar manner; placinguser data in the user data area of sector 464 of Erase Block N+Y 454 andthe associated overhead data in a sector 464 overhead area 458 of EraseBlock N 452 (for write/read sequence A, B, C, and D). In FIG. 4B, thefirst sequential sector of user data is written or read from the superblock 400 starting with the user data area 460 of Sector 0 of EraseBlock N+Y 454. The overhead data associated with the first sequentialsector of user data is then written to/read from the overhead data area458 of Sector 0 of Erase Block N 452. The second sequential sector (thenext sector) of user data written to/read from the super block 450 isthen written to/read from the user data area 410 of the next sequentialsector 464, Sector 1, of Erase Block N+Y 454 and the associated overheaddata is written to/read from the next sequential sector 464, Sector 1,overhead data area 458 of Erase Block N 452. User data and associatedoverhead data is written to/read from the erase blocks 452, 454 of superblock 450 in this manner until all the user data areas 460 of thesectors 464 of Erase Block N+Y 454 have been utilized or all utilizedsectors 464 read.

FIG. 4C is a simplified diagram of a super block pair 470 showing yetanother method of data write/read access sequences to an embodiment ofthe present invention. In FIG. 4C, the super block 470 contains a pairedset of associated erase blocks (Erase Block N and Erase Block N+Y) 472,474. Each erase block 472, 474 containing a sequence of erase blocksectors 484 having a user data area 476, 480 and an overhead data area478, 482.

When data is written to/read from the associated erase blocks 472, 474of the super block 470 of FIG. 4C, each sector of data is sequentiallywritten to/read from the associated erase blocks 472, 474 of the superblock 470 in a manner that alternates accesses to each erase block 472,474, similar in manner to the method of FIG. 4A. Thus, the next sector484 to be written/read in the super block 470 of FIG. 4C is selectedfrom the erase block 472, 474 that was not last written/read. However,the overhead data of the previous sector is always written to/read fromthe following sector so that the sector accesses are sequential and thusefficient, particularly for large sections of data.

For example, user and overhead data is written to/read from the superblock pair 470 of FIG. 4C in the sequence 486 (user data A, user data B,overhead A, user data C, overhead B, user data D, overhead C, user dataE, overhead D, user data F, overhead E, . . . , user data M, overhead K,user data N, overhead M, user data O, overhead N, user data P, overheadO, and wrapping around to overhead P in Sector 0) as shown. In FIG. 4C,the first sequential sector of user data (A) is written or read from thesuper block 470 starting with the user data area 476 of Sector 0 ofErase Block N 472, the overhead data of Sector 0 is not accessed at thistime. The second sequential sector (the next sector) of user data (B)written to/read from the super block 470 is then written to/read fromthe user data area 480 of Sector 0 of Erase Block N+Y 474. At the sametime the overhead data area 482 of the second sequential sector (thenext sector) (Sector 0 of Erase Block N+Y 474) is then simultaneouslywritten to/read from for the overhead data (o/h A) associated with thefirst sequential sector of user data (A). The third sequential sector ofuser data (C) written to/read from the super block 470 is writtento/read from the user data area 476 of Sector 1 of Erase Block N 472while the associated overhead data (o/h B) of the second sequentialsector is simultaneously written to/read from its overhead data area478. The fourth sequential sector of user data (D) written to/read fromthe super block 470 is then written to/read from the user data area 480of Sector 1 of Erase Block N+Y 474 while the associated overhead data(o/h C) of the second sequential sector is simultaneously writtento/read from its overhead data area 478. User data and associatedoverhead data is simultaneously written to/read from the sectors 484 oferase blocks 472, 474 of super block 470 in this manner until all theuser data areas 476, 480 of the superblock 470 have been utilized or allutilized sectors 484 are read. Upon reaching the final sector 484 ofErase Block N+Y 474, the final sector user data (P) is written to/readfrom the user data area 480 and the associated overhead data for theprevious sector (o/h O) is written to/read from the overhead data area482. The method of FIG. 4C then wraps around and writes/reads theassociated overhead data (o/h P) for the final sector 484 of Erase BlockN+Y 474 from the overhead data area 478 of Sector 0 of Erase Block N472. In the method of FIG. 4C, the total number of write or readoperations to write/read a sequential number of sectors from thesuperblock 470 is the total number of sectors to be accessed plus oneadditional operation to write/read the overhead data of the final sectoraccessed and not the two times the total number of sectors accessed thatother methods require.

FIG. 4D is another simplified diagram of a super block pair 470detailing the data access sequence flow of writes/reads of the method ofFIG. 4C. In FIG. 4D, the super block 470 contains a paired set ofassociated erase blocks (Erase Block N and Erase Block N+Y) 472, 474.Each erase block 472, 474 containing a sequence of 64 erase blocksectors/logical column pages having a user data area and an overheaddata area. Each erase block sector/logical page can contain one or morelogical sectors. The data access is shown sequentially alternating 488between the erase blocks 472, 474 as a data access increments during aread/write sequence to the super block pair 470. When the final eraseblock sector of the super block pair 470 is accessed, the method wrapsaround to access the overhead data from the first erase block 472. Thisallows the data splitting write/read access method of FIGS. 4C and 4D toaccess the data contained in the paired erase blocks 472, 474 of thesuper block 470 with only a single additional access over what would berequired over accessing the data in a pair of erase blocks in a non-datasplit Flash memory.

As stated above, many Flash memories support multiple logical sectors ordata words within a single physical column page sector (also known asthe physical sector), in particular NAND architecture Flash memoriestypically utilize this approach due to their generally higher memorycell density and larger column page sizes. FIG. 5 details an example ofa Flash memory column page sector 500 of a Flash memory device array ofan embodiment of the present invention. The physical column page sector500 of FIG. 5 contains 2112 bytes of data and is formatted to containfour 512-byte logical sectors 502. In addition, space is provided at thebeginning of the physical column page sector 500 for four ECC codes 504of 8 bytes each. A further 32 bytes 506 is reserved for use by the EBMfirmware or other system level usage. The four 512-byte logical sectors502 are sequentially addressed N, N+1, N+2, and N+3, where N is a baselogical sector address for the physical column page sector 500. The ECCcodes 504 of the physical column page sector 500 are sequentiallyaddressed N−4, N−3, N−2, and N−1 to allow them to store the ECC codesfor the four sectors of the previously addressed physical column pagesector (not shown). This allows the physical column page sector 500 tobe utilized in implementing the data write/read access of the method ofFIGS. 4C and 4D. It is noted that other physical column page sectorformats of differing data sizes, numbers of logical sectors/data words,and split data write/read access methods/patterns are possible andshould be apparent to those skilled in the art with the benefit of thepresent disclosure.

FIGS. 6A and 6B are simplified diagrams of a super block pair 600showing the sequence flow of the data write/read access of the method ofFIGS. 4C and 4D utilizing a multi-logical sector format of a physicalcolumn page sector, as shown in FIG. 5. In FIG. 6A, a superblock 600contains a pair of matched erase blocks (Erase Block A and Erase BlockB) 602, 604. Each erase block 602, 604 contains 64 physical column pagesectors 606 of four logical sectors 608 each. The 128 total physicalcolumn page sectors 606 are written to/read from in the manner detailedin FIGS. 4C and 4D. Each of the physical column page sectors 606 alsocontains four ECC codes 410 that correspond to the four logical sectors608 of the previous physical column page sectors 606. The data access isshown sequentially alternating 612 between the physical column pagesectors 606 of the erase blocks 602, 604 as a data access incrementsduring a read/write sequence to the super block pair 600. Within aphysical column page sector 606 data accesses are sequentiallyincremented from logical sector 608 to logical sector 608 until all havebeen accessed. When the next physical column page sector 606 is accessedthe ECC data 610 for the logical sectors 608 of the previous physicalcolumn page sector 606 is accessed. When the final physical column pagesector 606 of the super block pair 600 is accessed (from Erase Block B)and all the contained logical sectors 608 accessed, the data accessmethod wraps around 614 to access the associated ECC/overhead data 610for the logical sectors from the first physical column page sector 606of the first erase block (Erase Block A) 602.

In FIG. 6B, a simplified diagram showing the sequence flow of the datawrite/read access in a multi-logical sector format of a physical columnpage sector wherein the data access does not start and end on a physicalcolumn page boundary utilizing the method of FIGS. 4C and 4D. In FIG.6B, the addresses of the logical sectors start from a base address Nthat corresponds to the first logical sector 628 of physical sector 0 ofErase Block A 602. A data access starts on logical sector address N+1 ofphysical sector 0 of Erase Block A 602 and accesses logical sectors N+1,N+2, and N+3 616 of physical sector 0 of Erase Block A 602. The dataaccess continues in physical sector 0 of Erase Block B 604 and accessesECC N+1, ECC N+2, and ECC N+3 618 and the logical sectors N+4, N+5, N+6,and N+7 620. The ECC data for ECC N+4, ECC N+5, ECC N+6, and ECC N+7 622are accessed from physical sector 1 of Erase Block A 602 along with thelogical sectors N+8 and N+9 624. The data access is then finished byaccessing the ECC data for logical sectors N+8 and N+9 624, ECC N+8 andECC N+9 626 from physical sector 1 of Erase Block B 604.

It is noted that other manners of accessing a multi-logical sectorformat of a physical sector utilizing embodiments of the presentinvention should be apparent to those skilled in the art with thebenefit of the present disclosure.

FIG. 7, details a simplified diagram of an address control circuit 700of a Flash memory embodiment of the present invention. The addresscontrol circuit allows for automatic generation of sequential addressesgiven a starting address loaded into it by a processor or a memorycontroller, simplifying memory system address control in a datasplitting memory or memory system. In FIG. 7, two address registers 728,730 contain the addresses for accessing an Erase Block A and Erase BlockB of a superblock pair (not shown). Each address register 728, 730contain a row address register 712, 716 and a column address register714, 718. The address registers 728, 730 are coupled to an addressmultiplexer 710 that selectively couples each address register 728, 730to the interface 734 of a Flash memory subsystem, card, or individualFlash memory device (not shown). A register select circuit 704 iscoupled to the address multiplexer 710 and controls its operation. Anerase block size control circuit 724 is coupled to the row addressregisters 712, 716 and resets all or part of the row address registers712, 716 to control wrap around within the superblock to wrap accessaround to the first physical sector/column page of the superblock (thefirst physical sector of the first erase block, Erase Block A) after thefinal physical sector (the final physical sector of the second eraseblock, Erase Block B) has been accessed. A control circuit 702 iscoupled to a host interface (typically a processor or a memorycontroller) 732 and to the address registers 728, 730 by a Load 708,Increment Row 722, and Zero Column 720 signal lines that allow thecontrol circuit 702 to load the address registers 728, 730 with anaddress, increment the row address registers 712, 716, and zero thecolumn address registers 714, 718. The Load 708 signal line is alsocoupled to the erase block size control circuit 724, allowing thecontrol circuit to load an initial count into the erase block sizecontrol circuit 724. Both the Load 708 and a Toggle 706 signal lines arecoupled to the register select circuit 704, allowing the register selectcircuit 704 to be loaded with an initial selected erase block of thesuperblock pair and allowing the control circuit 702 to toggle theselected erase block address from the address registers 728, 730 that iscoupled to the Flash memory.

In operation of the address control circuit 700 of FIG. 7, the controlcircuit 702 loads an initial access address, which may or may notcontain an initial address offset in the selected column page (typicallyreflected in a non-zero column address), from a coupled host (not shown)to the address registers 728, 730 and the erase block size controlcircuit 724. The host accesses the coupled Flash memory/Flash memorysubsystem, which operates in a burst access mode, automaticallyincrementing the internally latched address for each read/write access.It is noted that the control circuit 702 may be adapted to operate thecoupled Flash memory in the absence of a usable burst mode of operation.The control circuit 702 tracks the number of accesses until the columnpage boundary of the current column page/physical sector of the selectederase block of the super block pair is reached (the highest addresseddata word/logical sector of the current column page is reached). At theend of a column page/physical sector the register select circuit 704 istoggled by the control circuit 702 to begin access in the next columnpage from the other erase block. The control circuit 702 increments therow registers 712, 716, in addition to toggling the register selectcircuit 704, when the column page boundary reached is the column pageboundary of the second erase block (Erase Block B). This wraps aroundthe access to the beginning of the next row of the superblock (the nextrow of the first erase block, Erase Block A). If the currently selectedcolumn page being accessed is the initial column page of the dataaccess, the control circuit 702 resets all or part of the column addressregisters 714, 718 to zero to eliminate the initial address offsetwithin the column page, when the column page boundary is reached. Thisinitial address offset is loaded with the initial address from the hostand is no longer needed after the first column page; if accesscontinues, the next address will start in the next sequential columnpage/physical sector at zero (the lowest addressed data word/logicalsector in the column page). Alternatively, the control circuit canautomatically reset the column page registers 714, 718 to zero upon eachcolumn page boundary being reached. It is noted that multiple Flasherase block addressing schemes are possible necessitatingsetting/resetting all or only a portion of the column address to zeroafter the initial page boundary (i.e., where the column page size doesnot match the size of the erase blocks of the Flash memory device). Itis also noted that in Flash erase block addressing schemes where thecolumn page size does not match the size of the erase blocks of theFlash memory device, the column address and row address registers mayneed to be incremented in a different manner than simply incrementingthe row address registers to address the next column pages of the eraseblocks of the superblock.

If the data access is at end of superblock (the last physical sector ofthe second erase block, Erase Block B) erase block size control circuit724 notes the final access (by the value of an internal register loadedby the initial address provided by the host) and resets the row addressregisters to zero to wrap around the data access (to the first physicalsector/column page of the first erase block, Erase Block A). This wraparound allows the data access to continue from the beginning of thesuperblock or simply allow for the access of the ECC data for the lastphysical sector of the superblock (last physical sector/column page ofErase Block B).

This design takes advantage of the structure of the Flash memory columnpage/physical sector addressing to generate the alternating erase blockaddresses required by data splitting and offloads this task from thememory controller/processor (host). The main interaction required by thehost is the loading of the controller circuit 700 with the initialaddress of the data access. It is noted that this controller circuit 700can be adapted to operate with Flash memory devices having differingaddressing schemes, erase block sizes, physical sector sizes/formats,and burst or non-burst access modes and should be apparent to thoseskilled in the art with the benefit of the present invention.

FIGS. 8A and 8B detail simplified diagrams of a split data ECC circuitof an embodiment of the present invention for both a read 850 and awrite 840 access. In FIGS. 8A and 8B, a split data ECC circuit 800 isshown in a write operation 840 and a read operation 850 on two physicalsectors 806 of erase blocks (Erase Block A 802 and Erase Block B 804) ofa superblock for the data write/read access method discussed in FIGS. 4Cand 4D utilizing the physical sector format of FIG. 5. The columnpage/physical sectors 806 of the erase block 802, 804 contain fourlogical sectors 808 and four ECC data codes 810 each. The four logicalsectors 808 of each erase block physical sector 806 are sequentiallyaddressed; N, N+1, N+2, and N+3 for the detailed physical sector 806 ofErase Block A 802, and N+4, N+5, N+6, and N+7 for the detailed physicalsector 806 of Erase Block B 804, where N is a base address. The four ECCcodes 810 of each erase block physical sector 806 are also sequentiallyaddressed and store the ECC codes for the four sectors of the previouslyaddressed physical sector/column page 806; ECC N−4, N−3, N−2, and N−1for the detailed physical sector 806 of Erase Block A 802, and ECC N,N+1, N+2, and N+3 for the detailed physical sector 806 of Erase Block B804.

In FIG. 8A, ECC circuit/hardware 814 under direction of control circuit812 is coupled to the sector data being written to the currently writeaccessed physical sector (in FIG. 8A, the logical sectors N, N+1, N+2,and N+3 808 of the detailed physical sector 806 of Erase Block A 802),during or after the logical sector write access. The ECC hardware 814generates the required ECC data for the user data written into thelogical sectors of the write accessed physical sector 806 and writesthem to a RAM storage circuit 818. When the next sequentially addressedphysical sector 806 is write accessed the control circuit 812 writes out820 the stored ECC data into the ECC code area 810 of the nextsequentially addressed physical sector 806 (in FIG. 8A, the ECC codeareas N, N+1, N+2, and N+3 810 of the detailed physical sector 806 ofErase Block B 804). This ECC generate, store, write process is repeatedby the split data ECC circuit 800 for each next sequentially writeaccessed physical sector 806 of the Flash memory/superblock.

In FIG. 8B, ECC circuit/hardware 814 under direction of control circuit812 is coupled to read 816 the sector data being read from the currentlyread accessed physical sector (in FIG. 8B, the logical sectors N, N+1,N+2, and N+3 808 of the detailed physical sector 806 of Erase Block A802). The ECC hardware 814 generates the ECC data for the user data readfrom the logical sectors of the read accessed physical sector 806 andtemporarily writes it to a RAM storage circuit 818. Before reading thenext sector, the ECC hardware 814 is loaded with the ECC data stored inthe RAM 818. Then when the next sequentially addressed physical sector806 is read accessed the control circuit 812 directs the ECC hardware814 to read 824 the stored ECC data from the ECC code area 810 of thenext sequentially addressed physical sector 806 (in FIG. 8B, the ECCcode areas N, N+1, N+2, and N+3 810 of the detailed physical sector 806of Erase Block B 804) and completes the ECC check for data errors. Inone embodiment of the invention, the ECC hardware will also attempt tocorrect the detected data errors before the read user data istransferred from the Flash memory. This ECC generate, store, compare ECCdata, and/or correct process is repeated by the split data ECC circuit800 for each next sequentially read accessed physical sector 806 of theFlash memory/superblock.

It is noted that other manners of writing and reading ECC data in splitdata single and multi-logical sector format physical sector Flashmemories utilizing embodiments of the present invention should beapparent to those skilled in the art with the benefit of the presentdisclosure.

It is also noted that other data write/read access sequences andcircuits for data splitting in embodiments of the present invention arepossible and should be apparent to those skilled in the art with benefitof the present disclosure.

CONCLUSION

Improved Flash memory device, system, and data handling routine havebeen detailed with a distributed erase block sector user/overhead datascheme that splits the user data and overhead data and stores them indiffering associated erase blocks. The erase blocks of the improvedFlash memory are arranged into associated erase block pairs in “superblocks” such that when user data is written to/read from the user dataarea of a sector of an erase block of the super block pair, the overheaddata is written to/read from the overhead data area of a sector of theother associated erase block of the super block pair. This datasplitting enhances fault tolerance and reliability of the improved Flashmemory device. Additionally, the performance cost of data splitting isminimized by the utilization of dedicated data splitting circuitry toautomate the reading and writing of user data and its associatedoverhead data into differing erase blocks of an erase block super blockpair. Furthermore, a method of partitioning data is shown forefficiently writing data in a distributed user/overhead data schemeformat.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement, which is calculated to achieve the same purpose,may be substituted for the specific embodiment shown. This applicationis intended to cover any adaptations or variations of the presentinvention. Therefore, it is manifestly intended that this invention belimited only by the claims and the equivalents thereof.

1. An erase block physical sector comprising: a user data area; and anoverhead data area, wherein overhead data stored in the overhead dataarea of the erase block sector is associated with user data of adifferent erase block physical sector.
 2. The erase block physicalsector of claim 1, wherein the erase block physical sector is adapted tocontain multiple logical sectors.
 3. The erase block physical sector ofclaim 2, wherein the erase block physical sector contains at least foursequentially addressed logical sectors of 512-bytes each.
 4. The eraseblock physical sector of claim 1, wherein the overhead data area isadapted to contain multiple logical overhead areas, wherein each logicaloverhead area corresponds to a logical sector of the different eraseblock physical sector.
 5. The erase block physical sector of claim 1,wherein the overhead data area is adapted to contain at least one errorcorrection code (ECC).
 6. The erase block physical sector of claim 1,wherein the user data area and the overhead data area have relativeaddresses within the erase block physical sector and wherein the userdata area has a relative address that is higher than the overhead dataarea.
 7. The erase block physical sector of claim 1, wherein the eraseblock physical sector is an addressed erase block physical sector m andwherein the overhead data stored in the overhead data area is associatedwith user data of an erase block physical sector m−1.
 8. The erase blockphysical sector of claim 1, wherein the erase block physical sector isan addressed erase block physical sector m and wherein the overhead datastored in the overhead data area is associated with user data of anerase block physical sector m+1.
 9. The erase block physical sector ofclaim 1, wherein the different erase block physical sector is in adifferent memory device than the erase block physical sector.
 10. Theerase block physical sector of claim 1, wherein the different eraseblock physical sector is in a different erase block than the erase blockphysical sector.
 11. The erase block physical sector of claim 10,wherein the different erase blocks are part of a superblock.
 12. Theerase block physical sector of claim 1, wherein the overhead datacomprises error checking data, a status flag for the sector or the eraseblock, redundant data, and/or erase block management data.
 13. The eraseblock physical sector of claim 1, wherein the sectors have the samesector address.
 14. The erase block physical sector of claim 1, whereinthe overhead data and the user data stored in the erase block physicalsector are accessed at substantially the same time.
 15. An erase blockphysical sector comprising: a user data area; and an overhead data area,wherein overhead data stored in the overhead data area of the eraseblock physical sector is associated with user data stored in a user dataarea of a different erase block physical sector; wherein overhead datastored in an overhead data area of the different erase block physicalsector is associated with user data stored in the user data area of theerase block physical sector; and wherein the user data area of the eraseblock physical sector and the overhead data area of the different eraseblock physical sector are respectively sequentially accessed for theuser data stored in the user data area of the erase block physicalsector and for the overhead data associated with the user data stored inthe user data area of the erase block physical sector and stored in theoverhead data area of the different erase block physical sector.
 16. Theerase block physical sector of claim 15, wherein the user data area andthe overhead data area of the erase block physical sector are accessedconcurrently.
 17. The erase block physical sector of claim 15, whereinthe different erase block physical sector is in a different memorydevice than the erase block physical sector.
 18. The erase blockphysical sector of claim 15, wherein the different erase block physicalsector is in a different erase block than the erase block physicalsector.
 19. An erase block physical sector comprising: a user data area;and an overhead data area, wherein overhead data stored in the overheaddata area of the erase block physical sector is associated with userdata stored in a user data area of a first different erase blockphysical sector; and wherein overhead data stored in an overhead dataarea of the first different erase block physical sector is associatedwith user data stored in a user data area of a second different eraseblock physical sector.
 20. The erase block physical sector of claim 19,wherein the erase block physical sector and the second different eraseblock physical sector are in a first erase block of an erase block pairand the first different erase block physical sector is in a second eraseblock of the erase block pair.
 21. The erase block physical sector ofclaim 20, wherein the user data area of the erase block physical sectoris a first accessed user data area of the erase block pair and the userdata area of the first different erase block physical sector is a lastaccessed data area of the erase block pair, wherein the user data areaand the overhead data area of the first different erase block physicalsector are accessed concurrently and wherein the overhead data area ofthe erase block physical sector is accessed sequentially after theconcurrent access of the user data area and the overhead data area ofthe first different erase block physical sector.
 22. The erase blockphysical sector of claim 20, wherein the user data area and the overheaddata area of the second different erase block physical sector areaccessed concurrently sequentially before the concurrent access of theuser data area and the overhead data area of the first different eraseblock physical sector.